Log Message:
graphics/simp: pull backend fix from git-hash

As of version 3.5.0, 'simp' defaults to Vulkan graphics, which NetBSD does not
support. In order to use OpenGL graphics we needed to set the environment
variable WGPU_BACKEND to 'gl', else simp would segfault when launching.

Commit 73500bc954dd8f740df701751a33d7d866f30970, two after the 3.5.1 release,
adds a secondary backend, falling back to OpenGL when Vulkan is not available.

So, we are no longer required to set the WGPU_BACKEND variable.